From 19dc5a25bc5c9af9e1fd3475f6642009348b0211 Mon Sep 17 00:00:00 2001
From: Zeitsperre <10819524+Zeitsperre@users.noreply.github.com>
Date: Fri, 6 Oct 2023 13:38:13 -0400
Subject: [PATCH] ignore invalid values in arccos calculation

---
 xclim/indices/helpers.py | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/xclim/indices/helpers.py b/xclim/indices/helpers.py
index e830decec..89673b00f 100644
--- a/xclim/indices/helpers.py
+++ b/xclim/indices/helpers.py
@@ -429,9 +429,10 @@ def day_lengths(
     lat = convert_units_to(lat, "rad")
     # arccos gives the hour-angle at sunset, multiply by 24 / 2π to get hours.
     # The day length is twice that.
-    day_length_hours = (
-        (24 / np.pi) * np.arccos(-np.tan(lat) * np.tan(declination))
-    ).assign_attrs(units="h")
+    with np.errstate(invalid="ignore"):
+        day_length_hours = (
+            (24 / np.pi) * np.arccos(-np.tan(lat) * np.tan(declination))
+        ).assign_attrs(units="h")
 
     return day_length_hours